The long-term objective of this research is to elucidate the role of stem cells in normal mammary gland development and tumorigenesis. Mammary stem cells are a population of self-renewing multipotent progenitor cells that can give rise to mammary specific alveolar, myoepithelial, and luminal cells. Mammary stem cells resemble cancer cells in their potential to self-renew for the life of an organism. The long-term self-renewal potential of stem cells makes these cells more susceptible to accumulating mutations that eventually give rise to tumors. The hypothesis of this research is that the mechanisms for self-renewal in normal mammary stem cells are similar to those employed by cancer cells. The specific aims of this proposal are to find markers for the identification and localization of stem cells within normal mammary gland and mammary tumors, to find novel genes and signaling pathways essential for the self-renewal of stem cells, and to determine the mechanism by which normal self-renewal pathways may be disrupted in mammary tumors. A combination of Stem Cell Antigen-1 (Sca-1), Hoechst staining, Rhodamine staining, and Breast Cancer Resistance Protein-1 (BCRP-1) antibody will be utilized to enrich for a population of self renewing, multipotent progenitors and to localize stem cells within the mammary gland and tumors. Cancer and normal stem cells will then be studied by subtractive hybridization, microarray analysis, and real time PCR to find additional novel mammary specific stem cell markers and to elucidate novel genes involved in their self-renewal. [unreadable] [unreadable]